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Walkthrough and analysis
Compute dp for each cell in the first example.
dp[2][1] = 1 (value 1, no smaller neighbors to come from). dp[2][0] = 1 + dp[1][0] = ? Need dp[1][0] first. dp[1][0] = 1 + max(dp[0][0], dp[1][1]). Continue...
Eventually: dp[2][1] starting with 1 → path through 2 → 6 → 9. Length 4.
Max over all dp values = 4.
Each cell computed once. time. Space: for memoization.
